Powered stringed instruments are prevalent. One of the most commonplace powered stringed instruments is the electric guitar. Typically, an electric guitar has six steel strings stretched between tuning machines (knob-gear arrangements for each of the strings), and a bridge where the strings terminate. On a solid body guitar, one or more electromagnetic pickups are disposed on the body of the guitar directly under the strings.
In order to amplify stringed instruments, the pickup converts string motion into a proportional voltage. A common type being used is an electromagnetic, inductive design. This type of pickup was originally developed in the 1930s and set the pattern for subsequent designs. The most basic type of inductive pickup uses a copper wire coil surrounding one or more permanent magnets. A representative pickup is shown in FIG. 1, which is a schematic representation of a spool assembly of a magnetic pick-up of a stringed instrument according to prior art.
Referring to FIG. 1, a spool assembly 10 typically includes a composite material that is used as a bobbin 11 to wrap electrical wiring coil 12. The number of turns in the coil 12 varies, in some embodiments the number is of the order of 6500 turns. The wires forming the coil 12 are generally made of copper with very thin (and fragile) polymer insulation. The coil terminates in wire-ends 13 and 14, which are respectively connected to (e.g., soldered) ends of the coil 12. The ends of the coil 12 are shown as white lines 16 and 18 for clarity. A plurality of permanent magnets 15 is positioned above the bobbin. The magnets 15 are generally made of Alnico, an alloy composed of aluminum, nickel and copper. Rare earth magnetic materials such as Neodymium or Samarium-Cobalt are also used, although seldom. Still other materials known in the art may be used.
The strings of the guitar (not shown) are positioned above the magnets 15. The electromagnetic field produced by the permanent magnet(s) 15 is normally stationary. However, the vibration of the steel strings disturbs the electromagnetic field and makes it vary. The interaction between the changing electromagnetic field or the changing magnetic flux and the stationary coil induces a time-varying voltage in the coil 12. The time-varying signal can be then amplified and played through speakers as sounds.
Pickup designers typically vary a small number of parameters in order to tailor the tonal characteristics. These are: 1) Diameter of coil wire; 2) Number of turns in the coil; 3) Magnet geometry; and 4) Magnet material. The relatively small number of design variables limits pickup designs.
Single coil pickups are sensitive to 60 Hz line noise in addition to string motion. As a result, a 60 Hz hum is often superimposed over the sound due to string motion. To overcome this undesired attribute, a dual pickup system, commonly known as the Humbucker design, was developed to take advantage of common mode rejection. The Humbucker design (not shown) includes two spool assemblies positioned adjacent one another in order to eliminate the 60 Hz hum (noise) that is induced into the coils.
Another design modification and evolution in the electric guitar technology is the addition of active circuitry to pre-amplify the signal at the pickup. Since the generated time-varying signals are low in power, traveling over a long distance before reaching the amplifier results in attenuation. By using a pre-amplifier at the pickup, the distance travelled and hence ohmic attenuation, prior to actively amplifying the signal at a main amplifier can be minimized.
It should be noted that conventional pickups are large and heavy. The presence of magnets and coils of copper wire can make these pickups excessively heavy for acoustic instruments and thereby these pickups are suited mostly to solid body electric stringed instruments. The size of the conventional pickup means that large pockets must be provided on the stringed instrument bodies to accommodate the pickup. Furthermore, conventional pickups are difficult to manufacture. Winding thousands of turns of wire that are as thin as human hair is difficult and time consuming. In many cases, the first 100-200 turns of the coil 12 can be shorted out by the pressure of successive turns of wire, thereby compromising the insulation. Also, it is difficult to make each coil identical, but build variation can result in a variation of sound, with all other conditions being the same. The coil wires can be microphonic. Also, the moving electromagnetic field sensed by the coil wire creates a force on both the moving wire as well as stationary wires in order to prevent the movement of the moving wire in the magnetic field. Unless the wire is firmly restrained, it can move and cause undesirable signals.
Therefore, a novel pickup arrangement for string instruments is needed that can be used as a kit in new instruments or to retrofit existing instruments to overcome some or all of the shortcomings of the prior art pickups.